Electric motors come in a variety of designs. Generally speaking, electric motors are driven by applying an electrical current to the inputs of the motor. The electric current then creates a magnetic field that turns the motor's rotor.
A motor can controlled by controlling certain aspects of the electric current applied to it. For instance, various controllers may include manual or automatic mechanisms for manipulating the electric current in order to start and stop the motor, select forward or reverse rotation, select and regulate the speed, regulate or limit the torque, protect against overloads and faults, etc.
A conventional approach for implementing current control when driving a direct current (DC) motor, for example, is Pulse Width Modulation (PWM). With PWM, a driving voltage is modulated by a square wave. The duty cycle of the PWM signal determines the average voltage applied to the motor, which in turn determines the amount of current delivered to the motor.